1. Field of the Invention
The invention relates to a method for pneumatic conveying of fine solids in the direct synthesis of alkylchlorosilanes, in which the conveying gas used is alkyl chloride, and to a method and apparatus for switching conveying gases in the pneumatic conveying of fine solids.
2. Background Art
The pneumatic conveying of solids, especially fine solids, has long been known (for example, Muschelknautz, E.; Wojahn, H., Chem.-Ing.-Technik, 46, 1974, 223-235) and is utilized whenever a high adaptation capacity of the conveying zones to the local circumstances is necessary, when environmentally friendly, closed conveying is necessary, and when a high flexibility of the distribution means, for example via pipe flow switches, is required. Another feature of pneumatic conveying is a low level of maintenance, and not least, pneumatic conveying offers the option of handling air-sensitive substances under a protective atmosphere.
For pneumatic conveying, gases such as air or nitrogen are typically used (see also W. Siegel, Pneumatische Förderung, Vogel Buchverlag, Würzburg, 1991, p. 71-72). Especially when combustible substances are involved, inert gases such as nitrogen or else argon are used.
In the direct synthesis of alkylchlorosilanes, fine solids or mixtures of solids are used, for example Si, catalysts or a mixture thereof, also referred to as catalyst composition. The reaction forms a spent catalyst composition which, as well as Si, includes distinctly elevated proportions of catalysts, promoters and secondary elements in the metallurgical silicon used. The direct synthesis of alkylchlorosilanes is described, for example, in EP 671402 A. Si grains, catalyst composition and spent catalyst composition are conveyed pneumatically in vessels and reactors in the alkylchlorosilane synthesis.